We are considering using Hevea rubber for some gloves, and we want to estimate what concentrations of n-butane will be after time of contact. The diffusivity is 1.5 x 10^-7 cm²/s. The initial concentration is zero, and the surface concentration at time zero is 2.4 kg/m³. Treat the diffusion as going into an infinite slab.

a. At 5 minutes, what will the concentration be at 6 mm into the slab?

b. How long will it take for the concentration at 10 mm to be 1.2 kg/m³?